Television system



May 1939. v. K. ZWORYKIN TELEVISION SYSTEM 2 Sheets-Sheet l INVENTOR: K. Zworg Ki r1,

RNEX

Vladimi r' 7d Time Original Filed July 17, 1 930 mmkmzb kwwtwbtou c HIS ATTO y 2, 1939. v. K. ZWORYKIN 2,157,048

TELEVI S I ON S YSTEM Original Filed July 17. 1930 2 Sheets-Sheet 2 INVENTOR.

5 Vladimir KZwo gKin, I F 3%08 HIS ATTORNEY FFiClr-I.

s'rarss PATENT SIGN SYSTEM Vladimir K. Zworykin, we: 0011,,1". 3., assigner, by mesne ents, to'Radio Cor- 'poratio'n' of Americm'New York, N. E, a cor-' poration oi Application July 17, I930, No..468,610-

13 Claims. (Cl. 178-733) My invention relates to improvements in tele ringelectronic emission. from the cathode, and vision systems, and it has particular relation to scanning the electrical image by a cathode ray systems of the type wherein the scanning devices; or beam to influence a circuit in a suitable radio at both the transmitter and receiver, are devoid orother transmission. system. of moving mechanical elements. My invention resides in an improved method 5 It has been. proposed, heretofore, to employ and apparatus of the character hereinafter defor television transmission a cathode ray'tube scribed and claimed. wherein the cathode comprises or is made up of For the purpose of illustrating my invention, a large number of relatively small photoelectric an embodiment thereof is shown in the drawings,

cells exposed to the cathode ray for scanning in which 10 thereby. This construction, while providing-for Fig. 1 is an enlarged fragmentary diagramsatisfactory results, has been found to introduce matic view of a television transmission system difficulties as regards practical construction of embodying the present improvements; the cathode unit. Prior art construction of the Fig. 2 is a diagrammatic -view of a television general type referred to isdisclosed by my cotransmission system embodying the present im-: 15

. pending application Serial No. 448,834, filed May provements;

1,.' 1930, assigned to the Westinghouse Electric Figs. 3 and 4' are graphical illustrations; and Manufacturing Company, Fig. 5 is a sectional view, the section being 4 One of the objects of the present invention, taken on the line 5-5 in Fig. 2;-

therefore, is to provide an improved method for Fig. 6 is an enlarged sectional view, the section 20 television transmission and apparatus therefor being taken on the line 6-6 in Fig. 5; which will not only avoid the dimculties referred Fig. '7 is an enlarged fragmentary view, showto in the construction proposed heretofore, but ing a modification;

' will be more satisfactory and produce better re- Fig. 8 is a section taken on line 8-8 in Fig. 7; sults in the way of possibilities for sharper'and, and 25 generally, better reception at the receiver. Fig. 9 is a. view similar to Fig. 1, showing a In accordance with my invention, an image modification.

of the object at the transmitting endis projected The cathode ray tube It! is provided with a onto a single photoelectric or light-sensitive single unitary photoelectric cathode il in the cathode, the occurring electron emission from the form of a fine mesh screen of suitable light- 30 letter is accumulated on an anode in the form sensitive material characterized by the fact that ofa relatively large number of small electrostatic electron emission occurs from a surface of the charges spaced uniformly over the area of the material when the same is exposed to light and anode and at relatively small distances apart, a at a rate which corresponds to and increases with cathode ray is developed and is caused to scan increase in light-intensity. 35 the anode and eflectsuccessive neutralization of A pair of relatively thin plate electrodes l2 these electrostatic charges during each scanning and I3 are supported as shown in spaced relacycle, and the charges are utilized to control the tion to each other and in planes parallel to the influence of the scanning ray with respect to a plane of the cathode ll. These electrodes are circuit in a suitable radio or other transmission provided with apertures through which tubular 40 system. insulating members l4 extend, as more clearly Further, in accordance with my invention, teleshown in Fig. 1. A plurality of metallic elements vision transmission is effected, in part, by acl5, having head portions l6 at one end thereof, cumulating electrostatic charges at spaced extend through the members Hi.

regions or spots over an area commensurate with An electrode IT, in the form of a fine mesh 45 the area of the image to be transmitted, the screen, is supported in the tube ID in close proxmagnitude of the charge at any region or spot, imity to the head portions l6.

at any instant, corresponding to the degree of The number and arrangement of the elements light-intensity at that instant on a correspondl5 are chosen-to suit particular conditions. For ing region or spot of the image. the purpose of transmitting an image or picture 50 Still further in accordance with my invention, framed in a five inch square, it is contemplated improved television transmission is provided for to employ sixty-four hundred of the elements l5 by projecting a light image of the object onto a and arrange the same uniformly over the area in single unitary light-sensitive cathode, developing eighty evenly spaced parallel rows, each row conan undistorted electrical image fromthe occurtainingeighty evenly spaced elements. 55

The tube I0 is provided with an electron gun I! of any suitable construction operable to develop a cathode ray or a beam of such rays and to project the same onto the elements 15. An example of the construction contemplated for the electron gun is disclosed in my co-pending application Serial No. 407,652, filed November 16, 1929, and assigned to the Westinghouse Electric and Manufacturing Company.

The cathode ray or beam is caused to scan the area within the image or pictureframe, there being, for example, twelve to twenty scannings of such area each second, the manner of scanning being such that the ray or beam strikes each region of such area at and immediately about each of the head portions l6 during each scanning cycle. In the present embodiment of my invention, the means or apparatus for such purpose is indicated as being of the well known type comprising, for example, coils l9 supplied by a 480 cycle oscillator 20 and plates 2| supplied by a 10 cycle oscillator 22, the coils l9 providing for horizontal deflection of the ray or beam of rays and theplates 2| providing for vertical deflection. This type of apparatus and the associated parts and connections thereforaredisclosed in more detail in my Letters Patent No. 1,691,324 of Nov. 13, 1928.

The electrode I 2 is connected to the positive side of a battery 23, while the cathode II is connected to the negative side of this battery. An electrostatic field is thus developed and maintained between the cathode H and the adjacent face of the electrode l2. The distance between adjacent faces of the cathode H and the electrode I2 is relatively small, that is, of the order of one eighth of an inch. The electrostatic lines of force are therefore parallel to each other and perpendicular to the adjacent parallel faces of cathode II and the positive electrode or anode l2.

The electrode I3 is connected as shown to the end 24 of a resistance 25, the other end of this resistance being connected to the positive side of the battery 23. r

The negative side of the battery 23 is grounded through connection 26. v

The electrode I1 is maintained at a fixed positive potential by connecting the same to the positive side of the battery 23 through .a connection 21. A battery 28 may be included in the connection 21 to'increase this potential if desired.

The input leads 29 and 30 of a suitable amplifier 3| are connected across the series-connected resistance'and battery 23. The output leads 32-and 33 of this amplifier are connected in the usual manner to the well known associated-apparatus and parts, all indicated by reference numeral 34,

of a suitable radio or other transmission system.

The image 35 of an object, indicatedby the arrow 36, is projected through a suitable lens or lens system 31 onto the light-sensitive surface of cathode II.

The manner or principle of operation of the present vtransmitting system is believed to be as follows:

Each of the elements l5 and the respective regions of electrodes l2 and I3 immediately about the same constitute a condenser which is continuously charged by the electron emission from cathode ll, indicated by the arrows 33. This electron emission develops at the light-sensitive surface of cathode ll upon which the light image is projected, the degree or rate ofsuch emission from any particular spot or point corresponding to and increasing with the light intensity thereon.

The entire number of electrons emitted from the light-sensitive surface of cathode ll reach the adjacent face of the composite anode. The electrons emitted from the regions or spots 42 of the light-sensitive surface reverse their direction of travel upon leaving this surface, under the influence of the electrostatic ileld,pass through the openings, in the cathode II and move toward the anode along the parallel electrostatic lines of force between the adjacent faces of the cathode II and the electrode [2, as indicated by the arrows 43. These electrons then leak to ground by way of the battery 23 and the connection 26. Electrons emitted from the regions or spots 40 between those designated by reference numeral 42 also reverse their direction of travel in like manner upon leaving the light-sensitive surface, as indicated by the arrows 4|, under the influ ence of the electrostatic field, move toward the anode along the parallel electrostatic lines of force between the adjacent faces of the cathode l I and the electrode I2, as indicated by the arrows 39, and contact with the elements 15, charging the same respectively to certain values as determined by the illumination of corresponding regions or spots 40 on the cathode II.

The charge curve of each condenser is shown in Fig. 3, wherein Es is the charge for saturation and Emaa: the maximum charge which any-condenser can receive under any conditions of illumination of the object. That is, where a particular region or spot 40 on the light sensitive surface of cathode II is one of the brightest spots of the image, the particular condenser of which the adjacent element I5 is a part will receive the maximum charge, Emax. No condenseris, therefore,

ever charged to saturation, the charging action always being confined to the straight-line portion of the charge graph, and between the limits zero and Emar. The manner in which this action is obtained will hereinafter more fully appear.

For the purpose of simplification, the influence or effect of the ray 44 of electrons from the source or gun ill will be considered in a given instance, as the same strikes one of the regions or spots 38 of the composite anode l3l5 during the scanning action or cycle of the beam of electron rays focused on and directed to this region or spot at the instant.

The electrons of the ray 44 reach the screen or positive electrode IT at a velocity corresponding to the potential difference between this electrode and the cathode 46. Part of these electrons strike the wire of screen I1 and are absorbed thereby and pass or leak to ground by way of the batteries 28 and 23 and the connection 26. The electrons which pass through the openings of the screen I! strike directly the region or spot 38 on the exposed face of the composite anode, part of these electrons striking the head portion 16 of element 15, the remainder striking the surface portion of the electrode l3 immediately adjacent or about the element l5, as indicated by the arrows at.

When all the elements H: are uncharged, or charged to the same potential, the same number of electrons strike each of these surface portions of the electrode l3 for all positions of the ray 44 with respect to the composite anode. Therefore, when there is no image on the light-sensitive surface of the cathode I l or in other words, when the illumination is uniform over such surface, the

electrons of the ray 44 contacting with the exposed surface of the electrode i3, as indicated by the arrows 44a, cause a direct current at constant voltage to flow through the resistance 25, and

number of electrons which reach any particular region of the electrode l3, as indicated by the arrows 44a, will vary under control of the charge E on the associated element l5. This variation in the number of electrons which reach any particular region of the electrode 13 will be inversely proportional to the value of charge E on the associated element l5 to which the ray 44 is directed at the instant, and, it follows, will be also inversely proportional to the magnitude of light intensity on the adjacent and corresponding region or spot 40 of the image 35. Variation in the number of electrons reaching any scanned region of the electrode I3 at any instant of the scanning period effects variation in or modulation of the initial direct current voltage across the resistance 25. The potential on the grid 41 of the amplifier 3| varies in accordance with such variation in voltage drop across the resistance.

The action just described is attributed to a negative field developed at the head portion l6 of each element I5, the field strength being determined by and varying with the charge E. This field has a retarding or opposing effect with respect to the entire number of electrons which pass through the screen l1. If the charge E is relatively small, this retarding eiiect or influence will also be small, and the number of electrons striking the electrode l3 will be correspondingly great. Conversely, if the charge E is relatively great, this retarding effect or influence will also be great, and the number of electrons striking the electrode l3 will be correspondingly small.

The full significance and advantage of the conditions in my present improved apparatus which allow or provide for storage or accumulation of the electrostatic charges E during a relatively large period of time, that is, during the entire period of the picture or scanning cycle of the ray 44, will be better appreciated upon comparison with conditions in television systems proposed heretofore. In these systems, the period of time during which the photocell or photocells of the transmitting apparatusare exposed to the influence of the light from each spot or region of the image is very short. For example, in such apparatus for transmitting a picture of one hundred lines with one hundred picture elements to each line, this period of time would be only 10- times the picture or scanning period. .If the scanning rate is twelve pictures per second, for example, the number of electrons released bythe photocell at any instant is measured by the photrons of light emitted in seconds from the particular spot of the object being scanned at this instant. It will therefore be appreciated that even for the brightest spot of the object, the number of light photrons available In my present improved apparatus, on the contrary, the light photrons emitted from each spot of the image are all eifective with respect to the light-sensitive part of my apparatus during the entire picture or scanning period, or in other words, for a period 10,000 times longer than has been the case in apparatus proposed heretofore. For similar conditions, therefore, the available or eiiective photoelectric current provided by the present improved transmitter is ten thousand times stronger than that in the prior construction referred to. 4

Those electrons of the ray 44 which strike the head portion l6 of the element 1 5 induce or cause emission of electrons from this element to the screen ll, as indicated by the arrows 49, to effect discharge of the charge E within the time Td. This electron emission is secondary with respect to that indicated by the arrows 39, 4| and 43. The electrons of the secondary emission thus drawn to or absorbed by the. screen I! pass to ground by way of the batteries 28 and 23.

The condenser charge E, by the action explained above, controls the extent or degree of influence of the ray 44 with respect to the electrode l3 in effecting variation in or modulation of the potential on the grid 41 of the amplifier, the amount of such variation being inversely proportional to the amount or magniture E of the charge. I

It will be understood that each of the condensers, of which the elements I5 are parts, are

. in effect, being continuously charged due to the continual electron emission from the light-sensitive surface of the cathode I l, collection of the charge taking place during the full period of the picture being transmitted, or in other words, during the full period of the scanning cycle of the ray 44. This period will be, for example, of

the order of one twelfth to one twentieth of a second.

The time allowed for each element I5 to accumulate its respective charge E is that elapsing between the times of succeeding contacts or impacts of the ray 44 on the particular region or spot 38 of the composite anode with which the element is associated. The scanning rate of the ray 44 is made so great that, although each element is is being continuously charged in the manner explained, the charging time To is never great enough to permit accumulation of a charge greater than Emaa: for the brightest spot or region of the light image. The graph of Fig. 4 is intended to represent a condition wherein Td is approximately one-twelfth of Te.

From the foregoing, it will be seen that an electrical image, in the form of a large number of electrostatic charges, is developed on the anode structure l3-l5, this image in effect being projected without distortion from the light-sensitive cathode ll upon which the light image 35 isprojected, the amount or degree of electrostatic charge E at any spot or region on the electrical image corresponding to and varying with the degree of light intensity on the respective adjacent spot or region of the light image. By scanning the electrical image with the cathode ray or rays 44, the potential on the grid 41 of the amplifier is varied or modulated in exact accordance with the different degrees of light intensity on the various spots or regions of the light image, the number of scannings each second being adequate to provide for satisfactory reception of a moving image at the receiver.

.As shown in Figs. 5 and 6, the electrode plates l2 and I3 may be clamped at their edges between complementary supporting rings 50 of suitable insulating material and provided with lugs 5| embedded in the wall of the tube ID. A spacing ring 52 of insulating material is interposed between the plates l2 and It, as shown. Screws or other suitable means 53 may be employed to clamp the rings 58 together.

As a modification, it is contemplated to substitute for the mesh cathode. a photo-sensitive semi-transparent film deposited on the inside face 64 of the tube I at the large end thereof. In such case, the image 35 would be projected upon the film to develop an electron emission corresponding to and efiective for the same purpose as that in Fig. 1, as represented by the arrows 39, 4| and 43.

The anode i 3-15 may be constructed in different ways to suit different requirements, each construction, however, being characterized by the fact that it will receive the electrical image developed at cathode I l and projected therefrom as indicated by the arrows 4| and 39. For example, in the construction shown in Figs. 7 and 8, the anode comprises two electrode sections or units 12a and-13a corresponding, respectively to the plates or electrodes l2 and I3 in Fig. l. Eachof the electrodes I20. and Ila is made up of a plurality of strips 54 of nickel or other suitable material. These strips are corrugated and arranged as shown, the engaging edges being secured tog'ether in any suitable manner such as by spot welding, as indicated by reference numeral 55. Tubular insulators Ha carrying the metallic inserts la extend through the openings 56 between adjacent strips 54, and have a close fit with respect to the latter.

The electrodes I2 and 13 in Fig. 1 may be combined'into a single electrode 51, as shown in Fig. 9. In this case, the action or principle of operation is the same as that in the arrangement or system of Fig. 1, the lefthand surface portion 58 of the electrode 5! corresponding to and func-' tioning in the same manner and for the same purpose as the electrode I2 in Fig. 1, the righthand surface portion 59 corresponding to and functioning in the same manner and for the same purpose as the electrode l3 in Fig. 1. The

single electrode 51 may be fabricated or built up in accordance with the modified construction in Figs. '7 and 8, in which case one of the sections I21: and l3a would be omitted.

It is contemplated to provide the tube III with an interior coating 60 of silver or other suitable material, over the area between the lines 6! and 62. This coating is electrically connected to the electrode l3 by a connection 63, and is therefore maintained at a positive potential. This coating, at a relatively high positive potential, creates an influence with respect to the cathode beam or ray to focus the same to a well defined spot on the anode l3-:| 5.

The tube I0 is evacuated to the highest possible degree.

From the foregoing, it will be seen that an improved method of television transmission has been provided wherein an electrical image is de- 1. In the art of television transmission, the method which comprises projecting an image to be transmitted upon a photoelectric cathode, accumulating the occurring electron emission from said cathode at regions spaced with respect to each other and disposed over an area commensurate with the image area, developing a cathode ray, scanning said regions with said. ray to initiate a secondary electron emission from said regions, and absorbing the electrons of said secondary emission by an anode.

2. In a television transmission system the combination with means for transmitting. picture signals of apparatus for developing such signals which comprises a source of cathode rays, a photoelectric cathode positioned remote from' said source, a first and a second electrode element arranged in a plane substantially parallel to the photoelectric cathode and separated from each other and from the cathode and located between the cathode and the source, a plurality of pinlike elements carried by and distributed over the said electrode elements, said pin-like elements being spaced with-respect to and insulated from each other and from the supporting electrodes, a third electrode element interposed between the pin-like elements and the ray source, and means for causing'the ray developed to simultaneously scan the said third electrode and the area over which the pin-like elements are distributed.

3. In a cathode ray tube, a source of cathode rays at one end of the tube, a substantially uniform photoelectric surface perforate to the free flow of electrons therethrough at the other end of the tube, a pair of plate-like electrodes arranged in spaced parallel relationship to each other and to the photoelectric surface and each interposed between the photoelectric surface and the ray source, a plurality of pin-like electrodes insulatingly supported from each other and from the plate electrodes carried by the plate electrodes and protruding therebeyond toward the ray source to be scanned by the developed ray, and a mesh-' like positive potential electrode located between the protruding pins and the my source whereby the developed ray in reaching the pin-like electrodes passes through the mesh.

4. In cathode ray apparatus of the character described, a tube provided with a first electrode having a light-sensitive surface and being perforate to the free flow of electrons transversely through the same, a second electrode disposed in proximity to and in substantially parallel relation to said first electrode, said second electrode being imperforate to the free flow of electrons transversely through the same and comprising a plurality of electrically-conductive elements insulated from each other and from said second electrode and each exposed on both sides of the latter, and means for developing a ray of electrons directed at said second electrode, said sec-- ond electrode being disposed between said means and said first electrode.

5. In a television transmission system, means for transmitting picture signals, means for developing picture signals and supplying the same to said first-named means;. said second-named means comprising a cathode ray tube provided with first, second and third electrodes supported in spaced and substantially parallel relation to each other, said first electrode having a lightsensitive surface and being perforate to the free flow of electrons transversely through the same, said second electrode being disposed between-said first and third electrodes. a plurality of electrically-conductive elements forming part of said second electrode and-each insulated from the same and from each other and each exposed on' for developing a ray of electrons directed at said third electrode and the adjacent side of said second electrode, said third electrode being perforate to the free flow of electrons transversely through the same; and means connected to and maintaining said second and third electrodes at a relatively high positive potential with respect to the potential of said first electrode.

6. In combination with a television transmission system, an electron tube including at one end thereof a mesh-like screen member, photoelectric material covering one side of said meshlike screen member onto which an optical image is adapted to be projected, means at the opposite end of the tube for producing an electron beam, a pair of plate-like electrodes positioned closely adjacent said mesh-like member and intermediate the mesh-like member and the electron beam source, and a plurality of collecting pin electrode members insulatingly supported between said plate like electrode members and each other and protruding therebeyond in the direction of the source of the electron ray whereby the electron ray when developed may be caused to scan said pin-like members.

7. In a cathode ray image transmitting tube, a source for developing an electron beam at one end of the tube, a mesh-like member positioned at the opposite end of the tube, said mesh-like member having a coating of photoelectric material upon one side'thereof upon which an optical image is adapted to be projected to cause the emission of electrons, a plurality of electrode, members positioned intermediate the mesh-like photoelectric member and the electron beam source, said members being adapted to have applied thereto voltages positive with respect to the electron source and to the photoelectrically coated mesh-like member, a plurality of pin-like members insulatingly supported between said plate-like electrode members and protruding therebeyond in the direction of the electron beam source for collecting the electrons emitted from the photoelectric mesh-like member under light activation, means for causing the developed electron beam to scan the said pin-likemembers to release the. collected charges thereon to initiate electrical signals representative of the light image falling upon the. photoelectric mesh-like member, and a screen electrode through which'the developed electron beam is adapted to pass posi tioned intermediate the ends of the pin-like members and the electron beam source.

8. A television system comprising an electron tube, means for producing an electronic scanning beam within the tube, an electrode member comprising a plurality of electrically isolated sections each of substantially elemental size, a light sensitive surface, means for producing on one side of the isolated sections of the electrode in accordance with illumination of the light sensitive surface an electrostatic charge image, and means for moving the produced electronic scanning beam across the opposite side of the isolated sections of the electrode member to discharge the stored electrostatic charges and thereby produce signalling impulses proportional to the light initiating the electrostatic charges.

-9. A television system comprising an electron tube, means for producing an electronic scanning beam within the tube, an electrode member comprising a plurality of electrically isolated sections each of substantially elemental size andhaving two exposed sides, a light sensitive surface, means for producing on one side of the isolated sections of the electrode in accordance with illumination .of the light sensitive surface an electrostatic charge image, and means for moving the produced electronic scanning beam across the opposite side of the isolated sections of the electrode member to discharge the stored electrostatic charges and thereby produce signalling impulses proportional to the light initiating the electrostatic charges.

10. A television system comprising an electron tube, means for producing within the electron tube a cathode ray scanning beam, an electrode member comprising a plurality of electrically isolated sections each of substantially elemental size positioned in the path of 'the developed cathode ray beam, insulating means for supporting each of the plurality of electrically isolated sections of the electrode member, a light sensitive surface, means for projecting an image of a subject upon the light sensitive surface for releasing photoelectrons and producing thereby on one side of the isolated sections of the electrode member an electrostatic charge image of the light image, and-means for moving the cathode ray beam across the opposite side of the isolated sections of the electrode to discharge the stored charges.

11. In a television system, means to produce an electrical current image of a light image, means to convert the electrical current image into an electrostatic charge image, and means for scanning the electrostatic charge image to produce signalling impulses.

12. In atelevision system, a photoelectric surface, means for illuminating the photoelectric surface with the light image of a subject of which a reproduction is to be produced at desired receiving points'so that there is released from the photoelectric surface an electrical current image representative of the light image, means for producing from the resultant current image an electrostatic replica and means for scanning the electrostatic replica to produce signals representative of the original optical image.

13. In a television system an electron tube, a photoelectric surface positioned within the electron tube, means for focussing alight image upon the photoelectric surface to produce a current image representing the light image, means for converting the produced current image into an electrostatic image, means for developing a cathode ray beam, and means for moving the cathode ray beam for scanning the electrostatic image to produce signals for transmission representative of the original optical image. 

